FIG. 20A is a perspective view of a conventional heat dissipating wiring board, and FIG. 20B is a sectional view of the same.
As shown in FIGS. 20A and 20B, conventional heat dissipating wiring board 101 has metal wiring plate 103, filler-containing resin layer 104 and heat dissipating plate 105. Metal wiring plate 103 forms a circuit pattern and has through grooves 102. Filler-containing resin layer 104 is embedded with metal wiring plate 103 such that the top surface of metal wiring plate 103 is exposed. Heat dissipating plate 105 is arranged on the under surface of filler-containing resin layer 104. The through grooves 102 are formed by punching of metal wiring plate 103 from the top surface to the under surface by pressing, and have a substantially vertical straight-line shape against the front surface of metal wiring plate 103.
Such heat dissipating wiring board 101 is capable of dissipating heat of an electronic component mounted thereon to heat dissipating plate 105 through filler-containing resin layer 104.
Therefore, also in a case where an electronic component is mounted with high density associated with fine-patternization, it is possible to suppress deterioration in thermal reliability of the electronic component.
It is to be noted that the patent document shown below can be cited as prior art document information concerning the invention of this application.
However, in the foregoing conventional heat dissipating wiring board 101, a space may be generated in through groove 102 that forms a circuit pattern due to incomplete filling with the filler-containing resin. Dust or the like may then get into this space portion, to cause deterioration in reliability against electric insulation.
This is because, since through groove 102 has a straight-line shape almost vertical to metal wiring plate 103, a flow channel of the filler-containing resin sharply narrows from the front surface of metal wiring plate 103 toward the inside of through groove 102, resulting in increased flowing resistance or increased tendency for clogging.
Further, the thinner through groove 102 becomes, or the higher a content of fillers becomes, the more the flowability of the filler-containing resin deteriorates, and the more significant the above-mentioned problem becomes.
Moreover, FIG. 21 is an expanded schematic sectional view of the conventional through hole. As shown in FIG. 21, since through groove 114 for the circuit pattern is formed by pressing, through groove 114 has a straight-line shape almost vertical to the front surface of metal wiring plate 115. Consequently, the flow channel of the filler-containing resin sharply narrows from the front surface of metal wiring plate 115 toward the inside of through groove 114, leading to deterioration in flowability.
Furthermore, the more through groove 114 is narrowed, or the more a content of fillers 122 is increased for improvement in thermal conductivity, or the more fillers 122 having different grain sizes are mixed in order to meet a request for fine-pitching, the more the flowability of the resin containing fillers 122 deteriorates, and the more significant the above-mentioned problem becomes.    [Patent Document 1] Unexamined Japanese Patent Publication No. 2003-152148